1. Field of the Invention
The present invention relates generally to the implant of prosthetic joints and pertains, more specifically, to the preparation of the distal femur for the implant of a femoral knee prosthesis, utilizing a femoral guide, such as a femoral sizing guide for the subsequent location of a femoral cutting guide, to assist in establishing the surfaces necessary for locating and securing the prosthesis in place on the femur.
2. Description of the Related Art
The implant of a prosthetic knee joint requires that the distal femur be prepared to receive the femoral component of the knee prosthesis by cutting the bone of the femur to establish accurately located surfaces against which the femoral knee prosthesis will rest upon implant of the femoral component. Various guides are available to the surgeon for assisting in guiding a saw blade during use of the saw blade to make the femoral cuts which establish the desired surfaces. These guides usually are located and secured on the distal femur, often upon a transverse surface established initially at the distal femur, to provide guide surfaces for guiding the saw blade during the execution of an axially directed anterior femoral cut, an axially directed posterior femoral cut, an anterior chamfer and a posterior chamfer, all specifically related to the size of the femoral knee prosthesis to be implanted and to the position and orientation of the femoral knee prosthesis at the site of the implant. The appropriate location of a femoral cutting guide, then, generally requires the use of a femoral sizing guide to determine the size of the femoral knee prosthesis which will be implanted at an implant site in a particular recipient, and to locate the corresponding femoral cutting guide appropriately on the transverse distal femoral surface for proper placement of the femoral knee prosthesis upon implant at the implant site.
Femoral knee prostheses are made available in a range of standard sizes. A femoral sizing guide is used to assist in the selection of a standard size femoral knee prosthesis which will best fit the requirements of a particular implant site. Once selected, the femoral knee prosthesis must be located and oriented so as to attain appropriate rotational alignment and create a symmetric flexion gap. Various intraoperative methods have been employed to determine femoral component rotation during knee arthroplasty. Among these methods are: (1) the use of the Whiteside line (line connecting the intercondylar notch and the patellar groove) as a reference; (2) the use of the transepicondylar axis (line connecting the high points of the epicondyles) as a reference; (3) the use of the posterior condylar axis (three degrees of external rotation off the posterior femoral condyles) as a reference; and (4) determining the femoral component necessary to form a symmetric flexion gap after ligament balance is complete in one or both of flexion and extension. It has been demonstrated that the use of the transepicondylar axis to determine femoral component rotation is, in most instances, the most reliable method for achieving the desired femoral component rotation.
The present invention provides a femoral guide and method and, in particular, a femoral sizing guide and method which facilitates the selection and orientation of a femoral knee prosthesis of appropriate standard size at a given implant site. As such, the present invention attains several objects and advantages, some of which are summarized as follows: Provides a single instrument for assisting a surgeon in the interoperative selection of a femoral knee prosthesis of standard size, and fitting the selected component for optimum position and orientation utilizing as a reference the demonstrated reliability of the transepicondylar axis; enables the surgeon to select and fit a femoral knee component of standard size at an implant site where the indicated size requirement does not coincide directly with a standard size, while still attaining optimum positioning and orientation of the implanted femoral knee prosthesis; enables an accurate and stable preparation for the appropriate size femoral knee prosthesis when the sizing procedure initially indicates a size which falls in-between standard available sizes; provides increased accuracy and stability in the location of a femoral guide at the distal femur; lessens the risk of creating an undesirable preparation at the distal femur; provides the surgeon with an advantageous technique for increasing the accuracy of the sizing procedure and concomitant accurate location of an appropriate femoral cutting guide, with added ease and lessened time; minimizes the need for guessing or for visual estimation in determining proper sizing and proper positioning of a femoral cutting guide, and especially proper rotational positioning, during femoral preparations for the implant of a femoral knee prosthesis; permits the surgeon to create a predictable and accurate femoral resection for exemplary performance in the completed implanted knee prosthesis.
The above objects and advantages, as well as further objects and advantages, are attained by the present invention which may be described briefly as a femoral guide for use in connection with the implant of a femoral knee prosthesis at an implant site at a distal femur of a femur extending in an axial direction within a recipient, the distal femur having a transepicondylar axis extending transverse to the axial direction, the femoral guide being arranged for engagement with the distal femur to enable interoperative determination of an optimum location and orientation of at least one femoral cut appropriate to accommodate the knee prosthesis at the implant site, the femoral guide comprising: a femoral block for engagement with the distal femur, the femoral block having a guide arrangement for determining the location and orientation of the at least one femoral cut; a support component for placement at a predetermined position relative to the distal femur; and a pivotal connection connecting the support component with the femoral block for pivotal movement of the femoral block relative to the support component about a pivotal axis extending generally in the axial direction and essentially intersecting the transepicondylar axis so as to enable orientation of the femoral block to rotationally position the guide arrangement for subsequent rotational orientation of the at least one femoral cut relative to the transepicondylar axis.
In addition, the present invention includes a femoral sizing guide for use in selecting a femoral knee prosthesis of a standard size for implant at an implant site at a distal femur of a femur extending in an axial direction within a recipient, the distal femur having posterior condyles with corresponding posterior condylar surfaces, a prepared distal femoral surface, and a transepicondylar axis extending transverse to the axial direction, the femoral sizing guide being arranged for engagement with the prepared distal femoral surface and the posterior condylar surfaces to provide a size indication for a femoral knee prosthesis of a size appropriate for the implant site, and enabling interoperative determination of an optimum location and orientation of an anterior cut appropriate to accommodate the selected knee prosthesis of standard size at the implant site, the femoral sizing guide comprising: a femoral sizing block having a block locator surface for extending transverse to the axial direction upon engagement of the femoral sizing block with the prepared distal surface, and a guide arrangement for determining the location of a femoral cutting guide to be placed subsequently at the distal femur for guiding execution of the anterior cut; a foot component including foot locator surfaces projecting in the axial direction for engaging the posterior condylar surfaces upon engagement of the block locator surface with the prepared distal femoral surface; and a pivotal connection connecting the foot component with the femoral sizing block for pivotal movement of the femoral sizing block relative to the foot locator surfaces to enable orientation of the femoral sizing block to locate the guide arrangement for subsequent placement of the femoral cutting guide in position to locate the anterior cut in a plane anterior of and essentially parallel to the transepicondylar axis.
Further, the present invention provides a method of utilizing a femoral guide in connection with implanting a femoral knee prosthesis at an implant site at a distal femur of a femur extending in an axial direction within a recipient, the distal femur having a transepicondylar axis extending transverse to the axial direction, the femoral guide being arranged for engagement with the distal femur to enable interoperative determination of an optimum location and orientation of at least one femoral cut appropriate to accommodate the knee prosthesis at the implant site, the method comprising: engaging a femoral block of the femoral guide with the distal femur, the femoral block further having a guide arrangement for determining the location and orientation of the at least one femoral cut; placing a support component at a predetermined position relative to the distal femur; and pivotally moving the femoral block relative to the support component about a pivotal axis extending generally in the axial direction and essentially intersecting the transepicondylar axis so as to enable orientation of the femoral block to rotationally position the guide arrangement for subsequent rotational orientation of the at least one femoral cut relative to the transepicondylar axis.
Still further, the present invention includes a method of utilizing a femoral sizing guide for implanting a selected femoral knee prosthesis of a standard size at an implant site at a distal femur of a femur extending in an axial direction within a recipient, the distal femur having posterior condyles with corresponding posterior condylar surfaces, a prepared distal femoral surface, and a transepicondylar axis extending transverse to the axial direction, the femoral sizing guide being arranged for engagement with the prepared distal femoral surface and the posterior condylar surfaces to provide a size indication for a femoral knee prosthesis of a size appropriate for the implant site, and enabling interoperative determination of an optimum location and orientation of an anterior cut appropriate to accommodate the selected knee prosthesis of standard size at the implant site, the method comprising: engaging a femoral sizing block of the femoral sizing guide with the prepared distal surface, the femoral sizing block having a block locator surface such that the block locator surface rests against the prepared distal surface and extends transverse to the axial direction, the femoral sizing block further having a guide arrangement for determining the location of a femoral cutting guide to be placed subsequently at the distal femur for guiding execution of the anterior cut; engaging a foot component with the posterior condylar surfaces upon engagement of the block locator surface with the prepared distal femoral surface, the foot component including foot locator surfaces projecting in the axial direction for engaging the posterior condylar surfaces; and pivotally moving the femoral sizing block relative to the foot locator surfaces to enable orientation of the femoral sizing block to locate the guide arrangement for subsequent placement of the femoral cutting guide in position to locate the anterior cut in a plane anterior of and essentially parallel to the transepicondylar axis.